Still wondering where to start looking about this bucking problem which occurs when the throttle is barely open. 2003 Baja, 5 speed, 77,000 miles. I put about 100 miles on the car today.

 

Is there any rudimentary test I can do to the TPS using an ohmmeter (measure resistance) or perhaps a 9V battery (voltage drop) to find out if there are any dead spots in it?

 

This bucking seems to be related to the throttle position. At cruise around 3000 rpms. Either drop the RPMS to 2000 or increase to 4000, the car runs smooth.

 

But still have not ruled out water in the gas. This problem cropped up 4 years ago after the car sat for 2 months in my garage. Since the CEL won't kick on, I have no idea where to start. I do know at times the check engine light will kick on but it says it's the air auxiliary valve which I think is just supposed to control the idle speed. The car idles fine and accelerates fine otherwise. I just clear the code and it goes away for about a year.

 

Seems the bucking get's worse after topping off the fuel tank or when the tank get's near empty, I still have not ruled out water in the fuel tank. Or ethanol in the tank absorbing the water. Reason being if I run the car for 20 miles, the problem seems to go away. As if I get the fuel and water in the tank gets agitated.

 

If I let the car sit for 2 weeks, it bucks for the first few miles. 

 

I have found water in the fuel tank on my lawnmower but in this case, it just blinded over the fuel filter.

 

Is there any way to drain the fuel tank? Any harm in disconnecting the fuel return line going back to the tank and run it into a gas jug until the engine dies or start to sputter?

 

Oh I have a new fuel filter by the way, fairly new plugs and plug wires.

 

Yes, two ways to test the TPS .

 

You can Either check voltage on the center pin with it still connected (easier IMO).

Or you can unplug the TPS and check resistance from the center pin to either outer pin.

Since digital meters often don't show a smooth change in voltage or resistance, it's usually best to check this with an analog meter so you can watch the needle for any quick jumps.

 

If you've been having this problem for years, water in the fuel is not likely.

Yes, two ways to test the TPS .

 

You can Either check voltage on the center pin with it still connected (easier IMO).

Or you can unplug the TPS and check resistance from the center pin to either outer pin.

Since digital meters often don't show a smooth change in voltage or resistance, it's usually best to check this with an analog meter so you can watch the needle for any quick jumps.

 

If you've been having this problem for years, water in the fuel is not likely.

 

I will check it out. Thanks.